The automated handling and moving of fabric webs has proved especially troublesome because of their porous nature. The drying of wet printing placed on such fabrics has also provided difficulties when undertaken by continuously operated machinery.
Fabrics, of course, have to varying degrees a porous nature. This permits the passage of air through them with at least some, if not a substantial, degree of facility. This passage of air through fabrics has interfered with or even precluded their handling in the fashion of nonporous webs such as sheets of paper. For example, the application of a vacuum to the upper surface of a sheet of nonporous paper permits its easy handling and movement. Turning off the vacuum allows, after some short delay, the placement of the piece of paper where desired. This vacuum control of the movement of sheets of paper has found especial use in printing presses and in the placement of labels in a plastic molding cavity for bottles and other containers.
Vacuum handling has encountered significant roadblocks in its application to the handling of porous fabrics. The initial problem occurs in lifting a single layer of fabric off of a stack. This happens, of course, in moving a piece of material off from a stack of such pieces. A dye cutting operation performed on a cutting table holding a vast expanse of a multitude of layers of virgin fabric may produce the stacks.
The application of a sufficiently strong vacuum to the uppermost layer of a stack of fabric materials will, typically, suffice to at least remove the upper layer. However, the porosity of that upper layer permits the vacuum to travel down to succeeding layers and cause them to lift with the top layer. The vacuum may suffice to cause both layers to travel to the same destination, for example a printing press. Alternately, the second and succeeding layers may simply drop crumpled in place or along the route of travel. In the former instance, it almost completely precludes any handling of succeeding layers. In the latter, it at least constitutes an economic loss and requires the consumption of time for its clean up.
Even the removal of a single layer of fabric from a supporting surface may also present difficulties. A strong vacuum, passing through the fabric, may cause the transporter to adhere through the fabric to the underlying support surface. Or, a sufficiently strong vacuum may initially also cause the fabric to move on the support surface and experience a distortion in its configuration when the transporting vacuum approaches.
U.S. Pat. No. 4,684,120 to N. Kamal shows various devices which place needles into the top layer or layers of fabrics in a stack in order to remove a predetermined number of them. However, accomplishing the objective has proved difficult and even requires, in one of the embodiments, unattached needles passing through the layers of material to keep successive layers from undesired motion.
R. R. Walton et al.'s U.S. Pat. Nos. 4,641,827 and 4,645,193 show pick-up devices having rectangular gripping elements which stretch the layer of fabric and nip the edges between them. They may use needles on their bottom sides to assist in the stretching and nipping process. The nipping, however, provides the actual gripping necessary to elevate the fabric. To assure that only one layer of fabric moves, the device may also incorporate a blast of air through the top layer of fabric to keep the next layer stationary. Additionally, the motion induced in the top layer of fabric by the gripping elements may help to reduce the adhesion between the top and adjacent layers of fabric.
In their U.S. Pat. No. 5,039,078, H. Blessing et al. utilized a staggered or "shingled" stack of cloth parts. While holding down the second and subsequent parts in the stack, the picker, perhaps using needles, pulls the top layer off the stack for subsequent utilization. Optical sensors determines the location of the different sheets. However, as suggested above, this device requires the shingling or staggering of the stack in a reasonably predictable manner in order to operate effectively.
Typically, when a fabric receives sufficient ink or other colorant to make a visible pattern, the amount of moist solvent will not readily dry in air. Stacking sections of fabric with wet ink will simply cause the pattern on one layer to transfer inappropriately to other layers. Thus, after receiving the ink, each layer of fabric must undergo drying prior to further handling.
The most typical fashion for drying a printed pattern on fabric has involved placing the piece of fabric into an oven for a substantial period of time. The oven itself, the energy to maintain it at an elevated temperature, and the space required to keep a conveyor line of fabric sections within the oven all substantially add to the expense of printing fabrics.
Furthermore, subjecting a printed fabric, especially those with a finishing, to the heat of an oven results in the shrinkage of the cloth. The evaporation of the moisture of the ink will cause an uneven heating of the fabric and the resulting shrinkage. Thus the fabric may undergo a "puckering" in the oven while it dries.
Oftentimes, a vacuum will hold a piece of fabric onto a surface while it undergoes printing or other handling. The porosity of the fabric requires a substantial vacuum to hold it down. To remove the fabric would typically involve turning off the vacuum. A nonporous sheet of paper cannot be removed without the vacuum's cessation. However, because of the size of the vacuum, its cycling on and off may not meet the time strictures of the processing equipment. Furthermore, turning it off results in the loss of the vacuum almost immediately and the inability to hold the fabric for almost any length of time subsequently.
Accordingly, the rapid and automated handling and printing of fabric pieces requires the development of devices for lifting a layer off a stack of webs, drying printing on a fabric, and lifting a piece of fabric off a surface where a vacuum holds it down. Accomplishing these tasks will permit the efficient and inexpensive handling and printing of fabrics.